Machine-driven railway switches used in North America generally use some combination of three different control rods: a throw rod, a detector rod and a lock rod. The throw rod applies forces exerted by the mechanical switch-positioning machine to the moveable rails to align or position them into the desired orientation or location. The lock rod is used to fix or lock the moveable rails securely in place after positioning, while the detector rod is used to indicate the position of the moveable rails to automated signaling systems. The rods typically occupy two adjacent cribs, or area between ties, with the throw rod being located in one crib and the lock and detector rods being located in the other crib. Cribs are normally filled with ballast in the absence of these operating rods.
The location of the rods in the cribs provides unobstructed access to the rods, in accordance with U.S. Federal Railway Administration and Transport Canada regulations relating to track construction and inspection. In order to maintain such unobstructed access and to avoid interfering with the operation of the rods, ballast is usually not provided in the cribs in which the rods are located. However the absence of ballast results in faster deterioration of the track geometry and stability. The problem is compounded by the fact that the presence of the rods in the cribs prevents mechanical tamping of the track near the rods. The inability to adequately tamp or compact the ballast combined with the reduced support and stability due to the lack of ballast results in rougher riding track, an acceleration of track wear and of damage to individual track components.
Changes in ambient temperatures cause steel rails to expand or contract with corresponding and potentially high forces. These forces may cause the rails to move along their length across the tops of the ties, thus carrying the attached control rods along the rails as they reposition themselves relative to the ties. This movement may force the rods into the side of the tie resulting in the rod rubbing against the tie surface. Such rubbing causes rapid deterioration of both the rods and the ties, sometimes resulting in electrical short circuits in the track signals. Additionally the interference between the operating rods and the ties may increase the forces required to reposition the moveable rails in excess of the force available from the switch machine.
In Europe, switches usually include several rods, for example a throw rod and two detector rods. In order to allow tamping and the use of ballast in the vicinity of the switch, and to protect the rod, it is known to seat the rod in a single hollow, channel-shaped metal tie, commonly referred to as a "hollow tie". This approach results in a hollow tie which is relatively wide. The widths of European style hollow ties would interfere with tamping equipment used in North America.
The desirability of a hollow tie concept compatible with the unique North American style of railway trackwork has been recognized for some time. However to date no practical implementation of the concept has been achieved. One perceived problem has been that an inordinately wide hollow tie would be required to accommodate the throw rod, lock rod and detector rod used in North American trackwork. Ties appreciably wider or deeper than the standard wooden or concrete ties presently used in North American trackwork or ties having little or no space between adjacent units will not allow mechanical tamping to be performed. Thus, any design for a hollow tie section should address the objective of allowing mechanical tamping in the area of the moving rail sections of the switch.
Other objectives in designing a hollow tie mechanism for moving rails and points include maintaining electrical insulation between the two rails and the switch machine and allowing for misalignment of the throw rods, lock rods, and detector rods due to thermal expansion of the rails to which the rods are attached. Additionally the hollow tie design should be adaptable to the manufacturing details of existing trackwork components to allow retrofitting, it should make use of unmodified switch machines presently in railroad inventories, it should be adaptable for use at multiple locations in a railway switch and it should provide mechanical assist rods in a multiplicity of locations within the trackwork component.
The foregoing objects are addressed by the present invention, which represents a successful application of the hollow tie concept to machine driven railway trackwork comprising throw rods, detector rods and lock rods. The hollow tie according to the invention provides unobstructed access to the rods for repair, adjustment or replacement, allows mechanical tamping near the moving rails, protects the rods during mechanical tamping operations, allows ballast in the cribs, and overcomes the problem of the rods rubbing against the ties while maintaining mechanical details and general geometry which are consistent with existing ties and cribs.